From GB 2 198 614 A an emergency stop system is know since long. In this publication there is disclosed an emergency stop system comprising a cut off means in the form of a primary control element, provided for instance to open a circuit breaker in the energy feed to a machine or to close a valve as a response to a remotely transmitted radio-sound- or ultrasound signal. Each operator carries a transmitter for transmitting this signal, such that the operator continuously is ready to rut off the energy feed in case of threatening situation or accident. There arc further suggestions for designing emergency stop systems, especially for designing said transmitter. Emergency stop systems hitherto known lack authority identification and authorization. This means, that the machines may be started even if no mobile units are in operation.
From US 2005/0055130 a communication system for wireless control is also known. In this, publication there is disclosed a portable operating unit and control unit. The portable operating units main purpose is to provide control of a machine but also execute an emergency stop on command or when the wireless communication is broken. This publication does not disclose or suggest, inter alia, driving means is provided not to be activated or inactivated without foregoing identifying and authorizing of the operator by IR-communication with the operators personal mobile control unit. This publication does also not disclose or suggest, inter alia, the application of such to be operated by several operators each carrying a device capable of wirelessly putting the machine unit into a safe state. This publication does also not disclose or suggest, inter alia, the operating unit to be able to control several machine units.